The use of catalytic converters in the exhaust system of automotive vehicles has caused attention to be given to means for retaining the high heat of exhaust gases as they are delivered to the catalytic converter. By delivering gases to the converter at very high temperatures, the light-off period of the converter, that is, the time required for the catalytic converter to reach its light-off temperature, can be shortened, resulting in less pollution being exhausted to the atmosphere.
The problem has been approached in the past by insulating the exhaust pipe between the engine manifold and the catalytic converter, primarily by substituting specially designed insulated pipe for the exhaust pipe normally employed. This requires the use of pipe which not only has the necessary insulating qualities, but which also is structurally capable of resisting the various stresses to which the pipe is subjected during normal installation and use.
An example of such pipe can be found in U.S. Pat. No. 4,345,430, which discloses a double pipe system comprised of inner and outer corrugated metal tubes with refractory fiber insulation in the space between the tubes. Although this arrangement is functional, it was found that vibration of the insulated exhaust tubing during normal use of the vehicle caused the refractory fiber insulation to be reduced to dust-like particles, thereby substantially eliminating the insulating properties of the material. Further, the need to make the insulated pipe strong enough to withstand the rigors of use has required that relatively heavy and rigid corrugated strips be used to form the corrugated tubes, making the pipe more expensive than desired.
In addition to the need to insulate exhaust gases for the purpose of efficient operation of catalytic converters, it would be desirable to be able to insulate other portions of the exhaust pipe system so as to function as a heat shield and to absorb exhaust system noise. The substitution of available insulated exhaust pipe for conventional exhaust pipe in order to accomplish these goals would, however, be quite expensive, and the insulated pipe would still not normally be as strong as conventional exhaust pipe.
It would be highly desirable to be able to insulate conventional automotive exhaust pipe in a simple, inexpensive manner instead of substituting new pipe for the conventional pipe. This should include the ability to insulate curved, angled and dimpled portions of the exhaust pipe as well as straight portions.